I have a 1990 inline 6 (4.9L 300 ci) 4x4

1) I want to upgrade my tires to a 31x10.5r15 from a 255/70r15 but I've been told by a few people that when you put bigger then factory tires you have to change the transmission and gear down the rear end to compensate for the bigger radius on the tires and wheels. Has anyone done this already (bigger tires)? If so then how did it effect/affect the power of the truck, fuel mileage, shifting and etc.

2) I want to level my truck and possibly a 4 inch lift. I've heard that it ruins the ride of the truck, is this true? I've did some research and Daystar claims that the factory ride will be maintained. Has anyone noticed a difference in the ride?

3) I want to change my Automatic Locking Hubs over to Manual Lockers. I don't know that much about the four wheel drive systems. What all would have to be replaced to make the change. Also does anyone know if these trucks are vacuum shift or electric shift for the four wheel drive?

4) I have a slight miss when the truck it is in Park and Neutral. When you put it in Drive or Reverse it's fine and there is no miss, I have already replaced: Plugs, Wires, Distributor Cap, Rotor Button, Air Filter and a newer fuel filter. I'm not sure what else it could be.


Thanks for all the help.

 

I'm currently running my i6 on 31x10.50 wrangler authorities with no problem at all. Mine has manual hubs manual trans and 3.08 non limited slip.

 

I am really interested in seeing the 255/70r15's on your truck. I am in the same boat as you but have 235/75r15's. I am thinking either 255/70r15's or 31x10.5's. I like the idea of getting a wider tread but I don't want to lose the power and actually like the height of the truck as is.

As far as gearing goes, depending on...well, everything, will tell you to regear or not. I asked a similar question last week and got the same answer. Some people can't stand the loss of drivability from 31" tires and others don't notice at all. It all depends on your personal preference.

From my experience in another vehicle (2001 Jeep Cherokee 4.0L lifted 3" on 31's from 235/75's) I did notice a change in drivability. At the time, it was my daily driver. Around town it was fine and doing some light off-roading it worked great. However, where I really noticed the fault in bigger tires was on the highway traveling over mountain passes. With any type of headwind or long ascent, I could feel the vehicle lugging a bit. Most of the time, it was corrected by taking it out of overdrive and settling into 3rd gear at a higher RPM.

If you have a pic of your truck I would love to see it.

 

The tires look amazing, I bought the truck with the 255/75r15s on it. They look super wide but without poking out the side. I don't know how to post pictures (i only know how to post
and do new threads but I'll be happy to send you some pictures.)
With the wider and therefore taller tires (after the fresh tune up) I'm managing about 20+mpg on the highway and about 15-16 city. As far as power loss it still has plenty of it (for the six) especially in 2nd and 3rd gear.

I know I want it to set up higher and poke out a little further.

 

Did you have to change it over from automatic hubs or did it come with the lockers?